We use the term "mutualized gold" when a gold bar is shared between several investors (generally 12.4 kg LBMA bars). Each investor owns a fraction of the bar. This is different from ownership in full name by which you are the sole owner of the bars or coins.
When investing in mutualized gold, you are exposing yourself to counterparty default risk (or intermediation). The bullion dealer or broker allots the bars amongst its clients and forwards a list of serial numbers and client numbers to the storage partner. The storage partner does not know the identity of the bullion dealer’s clients, and the storage certificate is issued in the name of the bullion dealer.
With mutualized gold, two problems arise with withdrawal. The first one is physical: a single bar is shared by several investors. In order to withdraw gold, one would have to smelt a large bar and make smaller ingots from it. This is a costly and time-consuming operation. The second problem is administrative and legal: since the storage company does not know the identity of the investor, it cannot give him/her access to the storage facility.
Mutualized ownership may be interesting in the context of a short-term speculative strategy. The platforms have made sell/buy orders automatic through a complex computer system that divides shares between users, offering them desired liquidity. This also allows lower administrative and handling costs. But the counterparty risk remains and, in an emergency, you will find it impossible to retrieve your stock. Owning mutualized gold does not offer the same guarantees as direct ownership of “allocated quantities”.